This invention relates generally to pneumatically powered screwdrivers of the automatic shutoff type. More particularly, this invention relates to an improved shutoff and reset mechanism for such screwdrivers.
Powered screwdrivers of various types and capacities are well-known and have been commercially used for many years. Popular among consumers of such tools are those specifically adapted to interrupt the power supply for automatic shutoff in contrast to those which slip or ratchet on encountering a turning resistance of preset torque value. Marketed tools exemplifying the shutoff type are disclosed in U.S. Pat. Nos. 2,964,151; 2,986,052; and 3,242,996, all of which have met with a large measure of commercial success.
While fundamentally similar in purpose, construction of the aforementioned shutoff tools is sufficiently different in order to render each of them operationally suitable for their specific use applications. As might be expected, tools suitable for torque sensitivity on the order of 40 inch pounds and above are substantially bulkier and heavier than such tools suitable for delicate work requiring torque sensitivities on the order of 11 inch pounds and below. Moreover, by virtue of their respective constructions, the higher torque tools are generally capable of high speed operation on the order of 3,000 rmp whereas the low torque tools have heretofore been subject to speed sensitivity causing them to endure low speed limitations on the order of 1,000 rmp. Where used for mass production assembly, tool speed is regarded as a significant factor in contributing toward the rate of production output. Consequently, it has long been desired to increase the speed of low torque tools, yet retain their compactness and light weight features compatible with use on delicate type work.
This invention is an improvement to the tool of U.S. Pat. No. 3,766,990. Occasionally, in the tool of that patent, the shaft would stop rotating when the clutch balls were on top of the cam lobes and with the release sear or pin apex engaging one of the points on the shaft end so that the supply valve could not be reopened to restart the tool until the balls and cam were repositioned manually. Such an occurrence did not affect the operational capability of the tool, but was an inconvenience that, in some instances, resulted in increased production time.
An object of the invention is to provide an improved powered screwdriver of the automatic shutoff type that also has a positive automatic reset capability.
Another object of the invention is to provide an improved reset mechanism for use in low torque powered screwdrivers.